The invention relates to a method for manufacturing glass plates of any contour from flat glasses, a separation line being driven, in a first stage, along a contour up to a predetermined depth in at least one side of a glass plate by means of a cutting device. Then, the glass plate is positioned and severed from the flat glass along the contour. The method is more specifically intended for manufacture of glass substrates for electronic storage media.
In addition to the method, the invention also provides a device for breaking glass plates of any contour out of flat glass. The device as well is more specifically directed to be used for manufacturing glass substrates for electronic storage media with an outside diameter and an inside diameter from a glass plate, such a device being comprised of a base pad and of a pressing facility.
Glass substrates for magnetic storage media, more specifically hard disks, are currently mainly made use of in laptop applications. The advantage of glass substrates over the currently widely used aluminium substrates lies in the increased rigidity, hardness, E-module and, as a result thereof, in the better resistance from impacts and the reduced fluttering.
Heretobefore, the applicability of glass substrates for magnetic storage media, more specifically hard disks, was made difficult because glasses with suited surface properties could only be provided with very high expense of technique.
This more specifically applies to the manufacturing of glass substrates by pressing and floating but also to glass ribbons manufactured by way of a drawing method as disclosed for example in U.S. Pat. No. 5,725,625.
With the drawn glass ribbons according to U.S. Pat. No. 5,725,625, the surface of the drawn glass must be subjected to two lapping steps and to two additional polishing steps.
A novel method as it is explained in the application Ser. No. 09/477,712, filed in the U.S. Patent Office on Jan. 5, 2000, the disclosure of which is fully incorporated herein, permits to achieve a drawn glass substrate that has a flatness ≦25 μm, more specifically ≦10 μm, a waviness <100 Å, more specifically <40 Å, a thickness variation of ±20 μm, more specifically +15 μm, and a surface roughness <10 Angström, more specifically <5 Å.
The surface properties, flatness, waviness and surface roughness are determined according to the known method like for example standard measurement methods for display substrates as described in SEMI D15-1296 of SEMI (1996). The term flatness is to be construed as the departure from an ideal flat surface measured over the entire surface, the term waviness as the mean wavelength part of the departure from an ideal surface related to a medium sized reference distance and the term surface roughness as the departure in the short wavelength range related to a short distance of measurement for evaluation. Such good surfaces need no longer be finished as this is for example the case with the surfaces according to U.S. Pat. No. 5,725,625. For glass substrates, it is therefore desirable to indicate methods for manufacturing electronic storage media with which the surface finishing process may be dispensed with altogether or be considerably reduced.
Current state of the art methods are not suited for further processing the drawn or floated glass ribbons with a flatness ≦25 μm, a waviness <100 Å, a thickness variation of ±20 μm, and a surface roughness <10 Å that must be cut so as to obtain smooth edges, with any predetermined contour of the cuts being possible and the surfaces being largely prevented from being damaged during processing.
One approach to avoid both slivers, recesses and microcracks is to separate glass on the basis of thermally generated mechanical stresses. The beam of a heat source directed onto the glass is thereby moved relative to the glass at a constant speed, a high thermomechanical stress which causes the glass to crack being generated in the process. This thermomechanical stress is further increased by a cooling spot that follows the heat beam. Infrared radiators, special gas burners and more specifically lasers meet the property requirement placed on the heat source which consists in being capable of locally positioning the thermal energy, i.e., of positioning it with an accuracy better than one millimeter, more preferably better than 100 micrometers, which corresponds to the typical cutting accuracies. Lasers have proved efficient and have gained acceptance because of their good focusability, the good controllability of performance and the possibility to form the beam and to thus distribute the intensity on glass. The glass is pre-scribed by the laser beam prior to being mechanically broken. This method is known as the scribe and break process.
Methods of laser cutting that induce a thermomechanical stress reaching beyond the resistance to breaking of the material by locally heating it through the focussed laser beam in connection with a cooling step from the outside have been proposed in EP 0 872 303 A2, DE 693 04 194 T2 and DE 43 05 107 C2 as well as in U.S. Pat. No. 5,120,926.
GB-A-1433563 shows a method in which a separation line is driven in a glass substrate using a laser, the glass being then broken along said separation line by means of a cutting device which is harder than glass. Examples of such type cutting devices are diamond or aluminium cutting devices.
An alternative scribe and break process is disclosed by U.S. Pat. No. 2,372,215. According to this method, a separation line of a depth T is scribed in a glass surface using a cutting tool, such as a small diamond wheel for example, and the glass is then broken by mechanical action along said separation line for example.
In a preferred embodiment, the glass is broken along the separation line T by introducing on purpose temperature stresses in the glass.
With the prior art scribe and break techniques, glass substrates, more specifically for electronic storage media, cannot be manufactured so as to meet the required quality more specifically because of their thickness.